One of the nicest qualities of using collets on the lathe is being able to run longer metal stock through the spindle bore, making multiple piece jobs far faster and easier, and making longer parts possible. The R8 collets will not let you do that. You will also have to use a drawbar to clamp the work, and have a means of stopping the spindle from turning while tightening the work in the collet. Having a work stop in the collet is not possible. The only real advantage I can see of having it is for holding pre-cut short pieces of stock for short run jobs, in a not very efficient manner. A three jaw chuck accomplishes essentially the same thing, but is easier to operate, and the stock can go through the spindle. Unless you have an ongoing need for doing a single job that fits those constraints, repeating it many times over, and have a plan to make the work flow go smoothly and quickly, I would not build one. Or maybe I am missing something???